Digestion

 The Human Digestive Tract

    Humans need nutrients and minerals from the foods we eat in order to remain in good health and survive. These nutrients and minerals are extracted from food and fluids by our digestive system in order to provide energy to our bodies. Digestion is a complex process that utilizes our digestive tract as well as other organs to aid with digestion. There are several components that make up our digestive system and they are responsible for different mechanical and chemical processes that contribute to the digestive process

We do not have to tell our digestive system when or how to breakdown the food we eat since it is run by our autonomic nervous system.  All we have to worry about is providing our bodies with nutrient rich foods. The purpose of our digestive system is to breakdown foods by acids and enzymes found in our digestive tract so that it can be absorbed by our bodies. As noted in the National Digestive Diseases Information Clearinghouse (NDDIC, 2013), “Digestion is important for breaking down food into nutrients, which the body uses for energy, growth, and cell repair. Food and drink must be changed into smaller molecules of nutrients before the blood absorbs them and carries them to cells throughout the body. The body breaks down nutrients from food and drink into carbohydrates, protein, fats and vitamins” (para. 3). Not only is the digestive system’s purpose important but its components as well.

  

The components of the digestive system are made up of our mouth, pharynx, esophagus, stomach, small intestine, large intestine and rectum/anal canal.  These components make up the mechanical part of digestion which includes tearing, chewing, mashing, squeezing and peristalsis. Other organs that aid with digestion as listed in The Digestive System: Part 1 include, “Accessory organs: teeth, tongue, three major pairs of salivary glands, liver, pancreas, and gallbladder” (Johnstone, Hendry, Farley & McLafferty, 2014, p.38).  These bodily components comprise the chemical aspect of digestion through which food is further digested by enzymes, acids, water, mucus, bile, and pancreatic juices. 

Mechanical aspects of digestion include the part of digestion involving any physical processes. This process starts the minute we put food into our mouth.  Our teeth break up food into small pieces we can chew (masticate) which stimulates the production of saliva.  It is noted in The Digestive System: Part 1,  “The tongue .... guides food during mastication, forming of the bolus or small ball of food and swallowing (deglutition), ... ” (Johnstone, Hendry, Farley & McLafferty, 2014, p. 38). The bolus then passes through the pharynx (throat), down the esophagus and into the stomach.  While the bolus is being processed, liquid from the upper portion of the stomach is release to help the bolus become liquefied.  The liquefied bolus is slowly squeezed into the lower portion of the stomach where it mixes with gastric juices to form chyme. This chyme is held in the stomach and slowly released to the small intestines through another sphincter muscle called the pyloric valve. The small intestines continues to add water and pass the chyme through by peristalsis until it reaches the large intestines. At this point most of digestion and absorption has taken place and the large intestine mainly reabsorbs water that was added earlier in the digestive process. It also absorbs minerals leaving only waste (feces) to be excreted. The large intestine passes the waste into the rectum where it is stored until excretion takes place (Sizer & Whitney, 2013). While the mechanical aspect of digestion involves physical actions like chewing and peristalsis, the chemical aspect of digestion involves the actions of enzymes and acids.

 

It is explained in the National Digestive Diseases Information Clearinghouse, “Digestive juices contain enzyme—substances that speed up chemical reactions in the body—that break food down into different nutrients” (para. 14). The following four organs contribute to the chemical aspect of digestion:

 Salivary glands: Food is moisten by saliva, which contains salivary amylase, an enzyme designed to break down starch into glucose (CrashCourse, 2012, video).

Stomach: Glands in the stomach lining produce stomach acid, which is a mix of hydrochloric acid and an enzyme called pepsin, as well as mucus and water. It is stated in The Digestive System: Crash Course Biology #28, “Hydrochloric acid has a pH of 1 which is extremely acid and aid in the breakdown of food and destroys bacteria found on food. The pepsin breaks down protein into amino acids. The mucus protects your stomach so that it doesn’t digest itself. ...The water assist to make all the food liquefy to help make the end product become chyme” (CrashCourse, 2012, video).

Pancreas: Provides several enzymes that break down carbohydrates, fats, and proteins in food and delivers these enzymes to the small intestines through ducts (National Digestive Diseases Information Clearinghouse, 2013. para 14).

Liver/Gallbladder: The Digestive System: Crash Course Biology #28 notifies us that, “The small intestine with the help of the gallbladder is to break down the fatty foods. On top of the small intestines is a little pipe where bile salts made by the liver and stored by the gallbladder are squirted out into the small intestine. Bile breaks down as an emulsifier, it takes hydrophobic fat molecules and breaks them up into fatty acids and monoglycerides, which can be absorbed by all that epithelial tissue ” (CrashCourse, 2012, video).

Small Intestine: The small intestine’s digestive juice mixes with pancreatic juice, bicarbonate, and bile to complete digestion. Protein breakdown is complete as well as the final breakdown of starches producing glucose molecules that the blood can now absorb. Carbohydrates are also digested in the small intestine by enzymes produced by bacteria (National Digestive Diseases Information Clearinghouse, 2013, para.20).

Large Intestine: Digestion is mostly complete by the time any remaining contents reaches the large intestines. Most of what is left is water, fiber and some minerals. Normal flora (bacteria) from the large intestines break down fibers that could not be broken by enzymes and the fat fragments released from the fibers are absorbed by intestinal cells for energy (Sizer & Whitney, 2013. p.85).

 The digestive system is a complex system that involves many components in the body.  These components make up the mechanical and chemical parts of digestion and work simutaneously in digesting and absorbing the foods we eat and fluids we drink.

References:

CrashCourse (2012, August 6). The Digestive System. [You Tube]. Retrieved from http://www.youtube.com/watch?v=Z7xKYNz9AS0&feature=related

Johnstone, C., Hendry, C. Farley, A. & McLafferty, E. (2014). The Digestive System: Part 1. Nursing Standard. 28(24). 37-45. Retrieved from the Ashford Library (EBSCOhost).

  National Digestive Diseases Information Clearinghouse (NDDIC). (2013). The Digestive System and How it Works. Retrieved from http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd/